It is the aim of the project to use the induction of tyrosine hydroxylase, (tyrosine-3-monooxygenase) in rat adrenal medulla as a model system to study the molecular mechanisms that control the expression of the genetic code by neurotransmitters activating post-synaptic receptors in target cells. We have provided the first evidence whereby acetylcholine released from pre-synaptic neurons increases the capacity of the cell nucleus to produce messenger RNA for tyrosine hydroxylase and other proteins. Moreover possible mechanisms that activate RNA transcription through phosphorylation of chromosomal proteins have been identified.